The present invention relates to disc drive data storage systems and, more particularly, to a low mass suspension formed by a pair of laterally spaced suspension beams.
Disc drive data storage systems use rigid discs which are coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor which causes the discs to spin and the surfaces of the discs to pass under respective hydrodynamic (e.g. air) bearing disc head sliders. The sliders carry transducers which write information to and read information from the disc surfaces. Each slider is supported by a track accessing arm and a suspension. The track accessing arms move the sliders from track to track across the surfaces of the discs under control of electronic circuitry.
The suspension connects the track accessing arm to the slider. The suspension provides a preload force, in the range of 0.5 gmf to 4.0 gmf, which forces the slider toward the disc surface. The preload force is generated by forming a preload bend in the suspension, which becomes elastically deformed when the track accessing arm, suspension and slider are loaded into the disc drive. The preload bend is typically positioned near the proximal end of the suspension, adjacent to the track accessing arm. The suspension has a comparatively rigid portion which transfers the preload force from the elastically deformed preload bend to the slider. The rigid portion is typically made by forming stiffening webs or flanges along the longitudinal edges of the suspension. Alternatively, the rigid portion may be formed by depositing circuit layers on the suspension material. The rigid portion of the suspension is typically referred to as a "load beam".
Additionally, the suspension is flexible in the slider pitch and roll directions to allow the slider to follow the disc topography. This pitch and roll flexibility is obtained from a gimbal structure, which is typically a separate piece part that is welded-to the load beam portion of the suspension. The separate gimbal is usually formed from a thinner material than the load beam to increase its pitch and roll compliance. Alternatively, the gimbal may be formed from partially etched material or from the load beam material itself. Partially etched gimbals are subject to wide variations in pitch and roll stiffness as the etched thickness varies -over a typical range. Gimbals formed from the load beam material restrict the suspension to be made of thin stock which can support only small preload forces.
The slider includes an air bearing surface which faces the disc surface. As the disc rotates, the air bearing surface pitches and rolls to an equilibrium position wherein a center of bearing pressure is defined on the air bearing surface. The desired location of the pressure center is defined as the air bearing load point. Variations in pitch and roll moments applied by the gimbal cause deviations in the location of the pressure center away from the desired air bearing load point.
The point at which the suspension applies the preload force to the slider is usually directly above the air bearing load point. The preload force is typically applied to the slider through a dimple or load button which bears on the back surface of the slider. Alternatively, the preload force is applied through the gimbal structure. This point of preload application is defined as the suspension load point.
Microactuators are now being developed for adjusting the position of the slider and transducer in an off-track direction. Either of the above methods of applying the preload force to the slider restricts the off-track motion of the slider at the suspension load point. When the preload force is applied to the slider through a dimple, the microactuator must overcome friction between the dimple and the slider surface to move the slider in the off-track direction. When the preload force is applied to the slider through a gimbal, the microactuator must overcome the off-track stiffness of the gimbal to move the slider in the off-track direction.
Improved suspension structures that are adapted for microactuation are desired.